US 8014479 B2
A system and method of communicating sub-synchronization information into a transmitted digital audio stream and extracting sub-synchronization information from a received digital audio stream is provided. The method includes the steps of having a transmitter introduce sub-synchronization information into a data stream at a period less than that of existing transmitter pre-amble signals, and transmitting that data to a receiver. The method further includes the steps of receiving the transmitted data stream in the receiver circuitry, extracting the synchronization information, and using the synchronization information to accurately decode the received audio data.
1. A method for communicating sub-synchronization information in a communication system, comprising the steps of:
generating a data stream comprising pre-amble information having a first period;
introducing phase-rotated sub-synchronization information into the data stream at a second period less than that of the first period of the pre-amble information, wherein a modified signal has a wobbling effect that is biased in a known direction;
transmitting the modified signal comprising the data stream containing the sub-synchronization information to one or more receivers;
receiving via one or more updated, coherent receivers the modified transmitted signal containing the sub-synchronization information, wherein the introduction of the sub-synchronization information comprises the sub-synchronization information modifying data in the data stream;
switching among a plurality of antennas, and passing the received signal from one antenna;
extracting the sub-synchronization information from the transmitted signal via the one or more updated, coherent receivers;
decoding the transmitted signal using the extracted sub-synchronization information via the one or more updated, coherent receivers, wherein the extracted sub-synchronization information is used to correct for at least one of phase and polarity ambiguity in the received signal, the phase ambiguities being resolved based upon the wobbling effect being biased in a known direction, wherein a quadrature (“Q”) bit ambiguity and an in-phase (“I”) bit ambiguity are resolved at different times, which allows for quickly switching among the plurality of antennas; and
receiving via one or more non-updated receivers, the modified transmitted signal, wherein the sub-synchronization information appears as noise,
wherein the Q ambiguity is solved by an algorithm comprising if Q data=1, then send I=I and Q=1, else send I=sign (I)*sqrt (2) and Q=0, and the I ambiguity is solved by an algorithm comprising if I data=1, then send Q=Q and I=1, else send Q=sign (Q)*sqrt (2) and I=0.
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12. A system for transmitting and receiving communication signals containing a sub-synchronization information having a period less than that of an existing pre-amble signal, comprising:
at least one communication signal transmitter for transmitting a modified signal comprising a data stream having pre-amble signals at a first period, the transmitter comprising
a phase rotator for introducing sub-synchronization information into the data stream at a second period, wherein the introduction of the sub-synchronous information comprises the sub-synchronous information modifying data in the data stream less than that of the first period, and the modified signal has a wobbling effect that is biased in a known direction;
at least one updated, coherent communication signal receiver for receiving the modified transmitted signal, the receiver comprising
a sub-synchronization correlator for extracting the sub-synchronization information from the signal received from the transmitter and
an antenna selector configured to switch among a plurality of antennas, and passing the received signal from one antenna, said receiver further decoding the transmitted signal using the extracted sub-synchronization information, wherein the modified transmitted signal is used to correct both an in-phase bit ambiguity and a quadrature bit ambiguity, the phase ambiguities being resolved based upon the wobbling effect being biased in a known direction, wherein a quadrature (“Q”) bit ambiguity and an in-phase (“I”) bit ambiguity are resolved at different times, such that the Q ambiguity is solved by an algorithm comprising if Q data=1, then send I=I and Q=1, else send I=sign (I)*sqrt (2) and Q=0, and the I ambiguity is solved by an algorithm comprising if I data=1, then send Q=Q and I=1, else send Q=sign (Q)*sqrt (2) and I=0, which allows for quickly switching among the plurality of antennas; and
at least one non-updated communication signal receiver for receiving the modified transmitted signal, wherein the sub-synchronization information appears as noise.
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The present invention generally relates to wireless digital communications, and more particularly, to injecting synchronization information into wirelessly transmitted signals received and decoded by digital transceiver systems in a format and at a rate sufficient to permit the effective use of fast diversity switching antenna systems.
Trucks, boats, automobiles, and other vehicles are commonly equipped with various signal communication devices such as radios for receiving broadcast radio frequency (RF) signals, processing the RF signals, and broadcasting audio information to passengers. Satellite digital audio radio (SDAR) services have become increasingly popular, offering digital radio service covering large geographic areas, such as North America. These services receive uplinked programming which, in turn, is rebroadcast directly to digital radios that subscribe to the service. Each subscriber to the service generally possesses a digital radio having a receiver and one or more antennas for receiving the digital broadcast.
In satellite digital audio radio services systems, the radio receivers are generally programmed to receive and decode the digital data signals, which typically include many channels of digital audio. In addition to broadcasting the encoded digital quality audio signals, the satellite service may also transmit data that may be used for various other applications. The broadcast signals may include advertising, information about warranty issues, information about the broadcast audio programs, and news, sports, and entertainment programming. Thus, the digital broadcasts may be employed for any of a number of satellite audio radio, satellite television, satellite Internet, and various other consumer services.
In vehicles equipped for receiving satellite-based services, each vehicle generally includes one or more antennas for receiving the satellite digital broadcast. One example of an antenna arrangement includes one or more antennas mounted in the sideview mirror housing(s) of an automobile. Another antenna arrangement includes a thin phase network antenna having a plurality of antenna elements mounted on the roof of the automobile. The antennas(s) may be mounted at other locations, depending on factors such as vehicle type, size, and configuration.
As the antenna profiles for the satellite-based receiving systems become smaller, performance of the antenna may be reduced. To regain this lost performance, multiple small directional antennas may be used that compliment each other. This type of antenna system relies on switching to the best antenna source for the signal reception. Another option is to combine the antenna with beam steering electronics. For low cost applications, a switched diversity antenna may be employed. In doing so, the RF receiver typically controls which antenna to use by detecting the presence of a desired signal.
Systems employing more than one antenna generally switch to another antenna when the signal from the current antenna is lost, or when the system determines that another antenna has a stronger signal. In a moving vehicle with frequently changing antenna orientations, it is often desirable to switch frequently and quickly among the various system antennas. When the system switches from one antenna to another, the system must acquire the new signal and process it to extract the audio or other data that is being transmitted. However, switching randomly causes the digital demodulator to quickly detect a new signal with an unknown phase. While the phase detector circuitry of many digital receiver demodulators will track the phase to a given position, the resulting data orientation generally will be unknown. Because of the unknown data orientation, it is not possible to correctly interpret the transmitted data.
The unknown phase/orientation problem discussed above can be resolved by transmitting a known data sequence into the data stream at predetermined times. This data sequence can be referred to as a synchronization signal, a pre-amble, or frame synchronization pre-amble (FSP). By first decoding the synchronization or pre-amble bits sent as part of the transmitted signal, the receiver can accurately decode the audio or other data that has been transmitted, and can reproduce that data for the user. However, the decoding of the synchronization bits must occur quickly in order to avoid a delay in the decoding of the audio or other transmitted data. This is because a delay in the data decoding may result in a loss of data, which in turn can result in audio mute for radio applications. To avoid this condition, synchronization data generally needs to be transmitted and received/decoded soon after a switch has been made to a new antenna.
Although some current satellite transmission/reception schemes provide for periodic transmission of synchronization bits to allow a receiver to ultimately decode transmitted data, the frequency of transmission of these synchronization bits is often too slow to allow for use in fast diversity switching antenna systems where rapid switching among antennas is required in order for the system to be effective. It is therefore desirable to provide for a transmission and reception system that provides for enhanced transmission and reception of synchronization information.
For purposes of this invention, the term “sub-synchronization” means having a time period less than an existing synchronization or pre-amble information (including signals and/or data). The terms “period” and “time period” refer to the amount of time between synchronization information.
In accordance with one aspect of the present invention, a method of communicating sub-synchronization information into a transmitted digital stream at a period of less than existing pre-amble signals already associated with that stream, and extracting sub-synchronization information from a received digital signal stream, is provided. The method includes the steps of generating a data stream including pre-amble signals having a first period, introducing phase-rotated sub-synchronization information into a data stream at a period of less than that of the existing pre-amble signal, and transmitting that data stream to a receiver. The method also includes the steps of receiving the transmitted data stream in the receiver, extracting the sub-synchronization information, and using the sub-synchronization information to accurately decode the received data.
According to another aspect of the present invention, a system utilizing sub-synchronization signals to accurately transmit and receive data is provided. The system includes a communication system transmitter that transmits a signal having pre-amble signals with a first period. The transmitter also includes a phase rotator that introduces sub-synchronization information into the signal at a second period less than that of the first period of the pre-amble signals. The system also includes a communication system receiver having a sub-synchronization correlator that receives the composite signal that includes sub-synchronization signals, and that extracts the sub-synchronization signals and uses them to accurately decode data.
In accordance with a further aspect of the present invention, a receiver capable of receiving sub-synchronization signals to accurately receive and decode transmitted data is provided. The system includes a communication signal receiver containing a sub-synchronization correlator for extracting synchronization information from a phase-rotated sub-synchronization signal. The system receives a signal having a pre-amble signal with a first period and sub-synchronization signals with a period of less than that of the first period of the pre-amble signal, extracts synchronization information from the sub-synchronization signal, and uses the extracted synchronization information to correct for errors.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Vehicle 100 is equipped with satellite receiver 40, including signal receivers, in the form of first and second antennas 30, for receiving radio frequency (RF) signals broadcast by any of satellites 10. One of the antennas 30 is shown mounted on the roof of the vehicle 100, and another antennas 30 is shown mounted on or in an exterior rearview mirror 31 of the vehicle 100. The antennas 30 could also be mounted on the tops of each of the two external rearview mirrors. It should be appreciated that any of a number of antennas and antenna arrangements may be employed on various locations of the vehicle 100, for receiving and/or transmitting signals to communicate with remote satellites and/or terrestrial-based communication devices.
The satellite transmitter 50 is illustrated in
The digital satellite receiver 40 employed on vehicle 100 is shown in
The receiver 40 is further shown including an analog-to-digital converter 42, a QPSK demodulator 43, a sub-synchronization correlator 48 for extracting sub-synchronization data, channel decoders 46, source decoders 47, and a controller 45 having a microprocessor 35 and memory 37. The microprocessor 35 may include a conventional microprocessor having the capability for processing routines and data, as described herein. The memory 37 may include read-only memory ROM, random access memory RAM, flash memory, and other commercially available volatile and non-volatile memory devices. Stored within the memory 37 of controller 45 are data and routines for selecting and processing received data. As is shown in
The operation of the satellite digital audio system is now discussed according to one embodiment of the present invention. As shown in
Modified transmit signals M, discussed above, have a predetermined length, and occur at a predetermined period that is less than the period of existing pre-amble signals generally transmitted by digital satellite transmitters. In addition, the modified transmit signals are created in a known and predictable manner, and can therefore be detected and interpreted by new receivers having the updated sub-synchronization correlator functionality discussed below. The modified transmit signals M can then be used by the receiver to correct for both the in-phase (I) bit ambiguity, and the quadrature (Q) bit ambiguity in the received signal. In the present embodiment, the Q ambiguity in the QPSK signal can be resolved by modifying transmit signals using the following exemplary algorithm: If Q data=1, then send I=I and Q=1, else send I=sign (I)*sqrt (2) and Q=0. The I ambiguity in the QPSK signal can be resolved by creating and transmitting modified transmit signals using the following exemplary algorithm: If I data=1, then send Q=Q and I=1, else send Q=sign(Q)*sqrt(2) and I=0. By using these exemplary algorithms for creating modified transmit signals M, a “wobbling” effect is created (due to the randomness of the data) that should be biased in a known direction, allowing phase ambiguities to be resolved by the receiver.
A timing diagram 61, shown in
After being transmitted via satellite dish 20 and one or more satellites 10, the transmitted signals are received by digital satellite receiver 40. Antennas 30, connected to the digital satellite receiver shown in
In another embodiment, similar to the embodiment shown in
The phase rotator 60 combines the sub-synchronization data from sub-synchronization controller 58 with the modulated signal from QPSK modulator 53 such that the resulting output signal contains sub-synchronization signals (also referred to as sub-frame synchronization pre-ambles or sub-FSPs) in a hierarchical layer separate from the primary signal layer. The sub-synchronization signals have a period that is less than that of the first period of the pre-amble signals. The digital output signal from phase rotator 60 containing sub-synchronization signals in a hierarchical layer is then provided to digital-to-analog converter 52 for conversion into an analog format for transmission. The analog signals are then passed from digital-to-analog converter 52 to antenna 51, at which point they leave the digital signal transmitter and are passed on to satellite dish 20 for transmission to one or more satellites 10. Controller 56, which in the illustrated embodiment includes microprocessor 65 and memory 67, along with a sub-synchronization injection routine 80, may be used to assist in the generation and injection of sub-FSP signals into a hierarchical layer, and their incorporation into the final transmitted signals. Digital signal transmitter 50 may also include a root raised cosine filter for filtering the signal from QPSK modulator 53 before it is processed by digital-to-analog converter 52, and upmixer circuitry between digital-to-analog converter 52 and antenna 51.
As shown in timing diagram 62 of
It should be appreciated that the satellite receiver shown and the satellite transmitter of the present invention will allow satellite transmission and receiver systems using multiple antennas to quickly switch from one antenna source to another using the sub-synchronization signals taught by the present invention. By providing and decoding sub-synchronization signals, the present invention advantageously provides the ability to rapidly switch from among several antennas without severely negatively impacting the quality of the audio received.
The above description is considered that of the preferred embodiments only. Modifications of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and not intended to limit the scope of the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the doctrine of equivalents.